Pathfinder: Kingmaker

Within a few weeks of acquiring your Barony, you should hear news that trolls are planning to attack your kingdom. Like the Stag Lord, this is a timed quest, so act with some speed. Also, you will need acid weapons unless playing on the weakest difficulty. You should be able to buy some in your capitol or use Octavia's acid splash. On Octavia, she needs point-blank-shot and precise shot to be effective. Make sure to equip your acid weapons when fighting Branded trolls. Fire weapons will also work on normal trolls, but only acid will stop Branded Trolls.

Go West from your capital to Ford at Skunk River and try to rescue Jubilost. If Jubilost is not there yet, you'll need to return later. Depending on choices and die rolls, he may not join you now, but later. Continue West to Ruined Watchtower and follow the dog to Ekundayo, the ranger. Convince him to join you and wait for the trolls. Ask Ekundayo for leads, and he'll give you three places to look for Trolls. Clear these areas.

While you're working on that, you should have a random encounter with a traveling merchant named Dalton. He'll point you to Bartholomew, a mage. Ask him about other dangers to find a goal for Armiri. Go to Bartholomew's Lone house. Watch for lots of traps, disarm them for XP. Talk to Bartholomew and kill a troll, then enter his lab. Loot this area and talk to the prisoner. Deal with the mage and the prisoner as you will. (Bartholomew has good stuff to sell, and good stuff, but different stuff, if you kill him)

Between Ekendayo and Bartholomew, you should now know the trolls are coming from the Dwarven Ruins. Take Harrim and Ekendayo with you when you go there to advance their quests, and Octavia or acid weapons to kill the trolls. Make your way through the dungeon. When Ekendayo tells you about Kargad, lure him outside for
When you get to the boss fight with Hargulka and Turtak, you'll have to make a choice. For the secret ending, kill Hargulka and interrogate Turtak about his curse. For you'll need to be Chaotic, and kill Turtak first. Then you can recruit Hargulka. Defeating both foes should unlock the achievement. If not, you may need to leave and return with Jubilost.